Authorities in India's capital have shut schools, halted construction and banned non-essential trucks from entering the city after air pollution shot up to its worst level this season.
Residents of New Delhi choked in a blanketing toxic smog as worsening air pollution surged past 60 times the World Health Organization's (WHO) recommended daily maximum.
So, why is this happening?
And can the annual toxic smog in India, Pakistan and Bangladesh be stopped?
How bad is the pollution?
The level of deadly PM2.5 pollutants in New Delhi — fine particulate matter in the air that causes the most damage to health — peaked at 907 on Monday morning, local time, according to IQAir pollution monitors.
A reading above 15 in a 24-hour period is considered unhealthy by the WHO.
"The people of Delhi are really troubled, they can't breathe," Delhi Chief Minister Atishi, who uses one name, told reporters on Monday.
"I kept receiving phone calls the entire night from people who had to admit their elderly parents to hospitals for breathing issues, or parents looking for steroid inhalers for their children," she added.
"The national government isn't doing anything. Today, the entire north of India has been pushed into a medical emergency."
Punjab, Pakistan's most populous province with 127 million residents, has been hit by a record-high ongoing wave of pollution since October.
"It's an apocalypse," said Ahmad Rafay Alam, a prominent environmental lawyer from Lahore.
Why is this happening now?
Air pollution in northern India rises every year, particularly in winter, as farmers burn crop residue in agricultural areas.
The burning coincides with colder temperatures, which trap the smoke in the air.
The smoke is then blown into cities, where emissions from cars, trucks and other vehicles add to the pollution.
Emissions from industries and the burning of coal to produce electricity also contribute to the smog.
Local weather and topography play a role too.
There are six major airsheds in South Asia: where pollutants from industry, transportation and other human activities get trapped so they cannot disperse easily.
Lahore in Pakistan, for example, is an airshed that contributes to cross-border pollution.
Under certain wind conditions, 30 per cent of pollution in New Delhi can come from Pakistan's Punjab province, where Lahore is the capital.
How have authorities responded to the latest smog?
In Delhi, classes for all grades except 10 and 12 will be held online and no trucks will be allowed to enter the city except for those carrying essential items.
Some older, diesel guzzling vehicles have been banned inside the city, and all construction activities have been halted.
Authorities also urged children, the elderly and others with chronic diseases or respiratory issues to avoid going outside as much as possible.
Similar measures have been invoked in the past, with authorities at times deploying water sprinklers and anti-smog guns in an attempt to control the haze.
But critics say there needs to be a long-term solution that drastically reduces pollution itself, instead of actions that aim to mitigate the effects after it has already plagued the region.
India's Supreme Court has ordered local authorities to take "all possible" action.
"It is the constitutional obligation of the central government and state governments to ensure citizens live in a pollution free atmosphere," the court said.
How are locals reacting?
The worsening air quality in India's capital has sparked outrage from residents on social media.
Many complained of headaches and hacking coughs, describing the city as "apocalyptic".
"Everyone has a sore throat," said Sanjay Goel, a 51-year-old shopkeeper in New Delhi.
"They should ban crop residue burning … it's just smoke everywhere."
Others urged officials to solve the public health crisis once and for all.
Several studies have estimated more than a million Indians die each year from pollution-related diseases.
Why has South Asia become the global pollution hotspot?
The worsening air pollution is an annual problem for South Asian nations as winter approaches and cold, heavy air traps pollution in a thick layer of smog.
IQAir's World Air Quality Report ranked Bangladesh, Pakistan and India as having the highest average PM2.5 concentration of anywhere in the world during 2023.
Countries in South Asia have seen major industrialisation and population growth over the past two decades, leading to increased demand for energy and fossil fuels.
And there are certain major contributors that are unique to South Asia including solid fuel combustion for cooking and heating, human cremation and burning of agricultural waste.
An increase in the number of vehicles on roads as the region has developed has also exacerbated the pollution problem.
In India and Pakistan, for example, the number of vehicles has increased four-fold since the early 2000s.
New Delhi, ranked the world's most polluted capital for four years in a row by IQAir, has 472 vehicles per thousand population, according to government data.
What is the solution to the pollution crisis?
South Asian countries have started trying to curb pollution, putting together air quality management plans, installing more pollution monitors, and pushing for a switch to cleaner fuels.
But these measures are yet to yield significant results.
Experts have called for greater cross-border cooperation among countries such as Pakistan, Bangladesh and India to address air pollution together rather than working in silos on a city-by-city basis.
Dust particles can travel hundreds of kilometres, transcending national boundaries and impacting countries other than those in which they originate.
About 30 per cent of the pollution in Bangladesh's largest cities, for example, originates in India.
Pratima Singh, who has researched air pollution in India for over a decade, said South Asian countries could emulate the European Union model of collaboration to deal with pollution challenges, formalise new policies and share data and best practices.
But it's a tall order when political relations in the region are fraught.
"There's a recognition among the technical and scientific community that air pollution doesn't need a visa to travel across borders," said Pakistani analyst Abid Suleri, from the nonprofit Sustainable Development Policy Institute.
The culprits and problems are the same on both sides of the India-Pakistan border, he said, so it makes no sense for one province to implement measures if a neighbouring province across the border isn't adopting the same practices.
ABC/wires
